1. Technical Field
The present invention relates to a phantom that indicates a dose of ultrasound beams radiated from an ultrasonic device used for measurement, diagnosis, medical treatment, or other purposes.
2. Prior Art
In recent years, great importance tends to be attached to the quality of life of a patient after medical treatment for a disease. In the case of serious diseases such as cancer, the social demand for minimally invasive therapeutic methods is also increasing. At present, endoscopic operations or laparoscopic operations that involve insertion of a tubular guide into the body or radio-wave cautery that involves insertion of a needle-like therapeutic instrument into the body are mainly employed as minimally invasive treatment techniques in clinical practice, although such techniques involve invasion of the body with an instrument. In contrast, ultrasound beams can converge in an area of 1 cm×1 cm or smaller in the body from the outside of the body without insertion of an instrument into the body, based on the relation between wavelength and attenuation inside body. With the utilization of such properties, clinical application of minimally invasive ultrasonic therapy has begun. At present, the most clinically advanced ultrasonic therapeutic technique is the high-intensity focused ultrasound (HIFU) therapy, which is targeted at treating hysteromyoma and breast carcinoma. This therapeutic technique involves irradiation of an affected area with high-intensity focused ultrasound (HIFU) to raise the temperature at the affected area to a protein aggregation temperature or higher within several seconds, thereby cauterizing the tissue at the affected area. In addition to HIFU therapy, the following ultrasonic therapeutic techniques are available; for example, sonodynamic therapy that involves cauterization of a target such as a tumor using active oxygen resulting from a phenomenon referred to as acoustic cavitation with the utilization of the interaction between a sensitizer and a ultrasonic beam and ultrasound-accelerated drug therapy, which is intended to accelerate drug efficacy by improving the ability of a drug to permeate an affected area with the use of ultrasound beams in combination with an existing drug.
In these therapeutic techniques involving the use of ultrasound beams, an ultrasonic generator is not brought into contact with the area to be treated. This requires monitoring of the area of treatment via a diagnostic imaging apparatus or the like. In addition to monitoring, it is important that a treatment plan be designed in advance so as to apply an adequate dose of ultrasound beams to the area of treatment and so as to prevent an inadequately large dose of ultrasound beams from irradiating areas other than the area of treatment, in order to more accurately perform selective treatment.
A treatment plan refers to predetermination of an area that is to be irradiated with ultrasound beams. In order to confirm the effectiveness of the plan and whether or not the apparatus would function as planed, it is required to prepare an ultrasonic phantom that can mimic a living organism and that is constructed to indicate the degree of ultrasonic irradiation. It is also necessary to irradiate the ultrasonic phantom with ultrasound beams to confirm the conditions of ultrasonic irradiation with the use of the ultrasonic phantom, prior to the application of the treatment plan to a human body.
Up to the present, an ultrasonic phantom that allows visualization of secondary actions resulting from ultrasonic application instead of ultrasonic energy has been devised as ultrasonic phantom as mentioned above. An example thereof is an ultrasonic phantom that uses a soluble protein as an indicator to detect temperature increase resulting from ultrasonic irradiation (C. Lafon et al., Proc., IEEE Ultrasonics Symposium, pp. 1295-1298, 2001). This utilizes the phenomenon whereby a protein is solidified and aggregated upon thermal denaturation, which increases the light scattering intensity compared with that before denaturation. Also, with the utilization of the phenomenon whereby a substance having a higher oxidizing power, such as a hydroxyl radical, is generated as a result of acoustic cavitation upon ultrasonic irradiation, a reaction substrate that develops color upon oxidation may be used as an indicator to detect the degree of chemical reactions caused by ultrasonic irradiation (JP Patent Publication (kokai) No. H04-332541 A (1992)).